VG436 Development of the fresh sweet corn industry to meet the requirements of Australian & export markets

Ross Wright, et al QHI, QDPI & Pacific Seeds

danikahStamp

VG436

This report is published by the Horticultural Research and Development Corporation to pass on information concerning horticultural research and development undertaken for the vegetable industry.

The research contained in this report was funded by the Horticultural Research and Development Corporation with the financial assistance of the QFVG.

All expressions of opinion are not to be regarded as expressing the opinion of the Horticultural Research and Development Corporation or any authority of the Australian Government

The Corporation and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in tills report and readers should rely upon meir own enquiries in making decisions concerning their own interests.

Cover price: $20.00 HRDC ISBN 0 7341 0049 3

Published and distributed by: Horticultural Research & Development Corporation Level 6 7 Merriwa Street Gordon NSW 2072 Telephone: (02) 9418 2200 Fax: (02) 9418 1352 E-Mail: hrdc@hrdc.gov.au

©Copyright 2000

HRDVC

HORTICULTURAL RESEARCH & DEVELOPMENT CORPORATION

Partnership in horticulture

mailto:hrdc@hrdc.gov.au

FINAL REPORT

HRDC

PROJECT VG436

July 1,1994 to June 30,1997

Development of the fresh sweet corn industry to meet the requirements of Australian and export

markets.

Ross Wright, Ian Martin, Terry McCarthy, Jeff Barnes, Reg Gounder (Queensland Department of Primary Industries)

Errol Corson & Graham Schull (Pacific Seeds)

Funded by

Queensland Fruit and Vegetable Growers (QFVG) and

the Horticultural Research and Development Corporation (HRDC)

INDUSTRY SUMMARY

• Field days and seminars in the major regional fresh sweet corn production areas of Gatton and Bowen allowed industry members the opportunity to view all new varieties developed through breeding efforts in Australia as well as introduced varieties from overseas. Information on future development of varieties and industry issues were also discussed at these forums.

• With a major part of the Queensland industry based on a limited number of temperate varieties, the identification of new temperate supersweet varieties with improved disease resistance through regional testing was a significant outcome. The rapid industry adoption of the variety Gladiator to complement the industry standard Goldensweet, over the duration of the project, demonstrated the need by industry for robust disease resistant varieties of good quality.

• The high level of leaf disease pressure at Bundaberg highlighted the need for improved levels of rust and leaf blight resistance in temperate varieties. While the new temperate variety Gladiator withstood the disease pressure well, the only other types to do so were the tropical hybrids. Further development of the industry in this area will be dependant upon availability of a wider range of good quality varieties with improved disease resistance.

• Major improvements in cob quality and virus resistance in tropical sweet corn hybrids developed at Kairi was demonstrated at Gatton by the identification of the new hybrid H141. Further development of the tropical types will provide excellent disease resistant hybrids with superior fresh market qualities to the only available virus resistant hybrid H5.

• New hybrids between tropical and temperate types developed at Gatton were demonstrated in the promising variety Pac377. Future combinations of the best of the tropical material with good quality temperate material will provide varieties more suited to production areas in Queensland.

1

TECHNICAL SUMMARY

• The project revolved around the development of the fresh sweet corn industry through the area of plant improvement, seen as the area of greatest opportunity. It provided a snapshot of the status of the industry in regional Queensland, the direction in which the industry was moving through plant breeding and varietal development and identified future opportunities.

• The narrow pool of shrunken-2 hybrids with the required horticultural suitability and disease resistance which are adaptable to fresh sweet corn production through regional Queensland was identified early in the project. While some increase in this pool unfolded over the term of the project, the need for further development in plant improvement efforts is obvious.

• The improvement in both disease resistance and eating quality available within the tropical germplasm was demonstrated in the new tropical hybrid H141. This provides encouragement for further development of elite tropical inbreds for future hybrid production.

• The first of the tropical x temperate hybrids demonstrated the potential for future development of this strategy. Further introgression of material with tropical and temperate backgrounds can be expected to produce high quality hybrids exhibiting excellent disease resistance.

• Additional industry development issues which emerged over the term of the project were in the area of plant emergence and establishment of shrunken-2 hybrids and the issue of heliothis management in sweet corn.

2

1. INTRODUCTION

Australian sweet corn production, both fresh and processed, has grown from almost 50,000 tonnes in the early 1990's to around 75,000 tonnes in the mid 1990's. The major producers are New South Wales with some 60% of production and Queensland with 20% of production (ABS). With total Australian demand estimated at 110,000 tonnes and domestic production not meeting this, imports of sweet corn, mostly as frozen product from New Zealand and the United States, are substantial (Smith, 1997), making Australia the fourth largest importer of sweet corn in the world (McMahon and Corsan, 1997).

The fresh sweet corn industry in Australia is relatively undeveloped. Per capita consumption of fresh sweet corn is low at around 4kg, about half that in the United States (Pataky and Mosely, 1995). In the USA, sweet corn is the third most consumed vegetable whereas in Australia it is the ninth most consumed vegetable (Pullar et al, 1993). Production in southern states is limited by shorter growing seasons while Queensland, with potentially longer growing seasons, is well suited to filling the production gaps and replacing a substantial portion of imported processed product with fresh sweet corn.

The industry is based on supersweet temperate cultivars which are less suited to production in the warmer months of tropical and subtropical Queensland. Many temperate corns have been of no value in the tropics where they grow very small with low leaf number and extreme earliness (Brewbaker, 1981). He found in tropical Hawaii all maize lines tested show some photoperiod sensitivity when comparing 12 and 16 hour days in the field. However, phenology studies in subtropical Bundaberg and Gatton in Queensland found that temperature was the most important factor contributing to development rate and photoperiod did not influence rate in the group of tropical and temperate hybrids which contained supersweet, (sh2) sugary extender (se) and sugary (su) types. (Olsen et al, 1993) In a separate study at Bundaberg, performance results for 6 temperate supersweet corn cultivars at three separate planting dates suggested that supersweet (shrunken-2 or sh2) cultivar production should be limited to a midwinter sowing in subtropical Bundaberg because of higher disease incidence and heat stress encountered in later plantings. (Olsen et al, 1990).

The fresh market sweet corn industry in Queensland has been heavily dependent upon temperate sh2 germplasm imported from the United States. The Snowy River Seeds Cooperative Ltd has been the major supplier of seed to this industry and has maintained a sweet corn breeding program for some years. The company produces hybrid sweetcorn from temperate inbreds imported over the years and has exclusive Australian rights to inbreds from the Crookham Seed Company in the United States. While widespread testing of hybrids is undertaken by the company in the major sweet corn growing areas, adaptation to subtropical and tropical environments during the warmer periods of the year is often not satisfactory. The temperate hybrids often lack resistance to leaf blight Exserohilum turcicum, some are susceptible to common rust Puccinia sorghii and all lack resistance to the major virus disease, Johnson Grass Mosaic Virus JGMV. This virus affects sowings from November onwards in Queenslands largest sweet corn production areas of the Lockyer and Fassifern Valleys. Occasional incidence of JGMV has also occurred in the Bowen region.

Low tolerance to high temperatures, low seedling vigour and inadequate husk cover in some temperate hybrids have also been of concern to growers in the industry. An existing Queensland Department of Primary Industries sweet corn breeding program at Kairi Research

3

Station on the Atherton Tablelands conducted by Ian Martin and Terry McCarthy had developed sweet corn lines with tropical adaptation. This material imported from Hawaii inherently had resistance genes to the virus JGMV and reasonable resistance to the leaf diseases which troubled sweet corn in the various vegetable production areas of Queensland. In conjunction with Plant Pathologist Denis Persley, upgrading of these disease resistances as well as improved seedling vigour was carried out using recurrent selection programs.

The fresh sweet corn industry in Queensland is serviced by the major production areas of Bowen-Burdekin, Lockyer Valley, and Bundaberg. While the Lockyer-Fassifern is the largest sweet corn production area, the bulk of the crop is processed. The major area for fresh market production is the Bowen-Burdekin region with a gross annual value of $5.8 M (A.B.S.). The Lockyer Valley fresh market crop is valued at $1.7 M, followed by the Bundaberg area valued at $0.6 M (Deuter, 1995). The Queensland crop is mostly marketed domestically throughout the major capital cities of Australia as well as being exported , mainly to New Zealand. The Australian market demands yellow sweet corn cultivars with no demand for bicolour types whereas the New Zealand market accepts both types. The Japanese market mainly demands bicolour cultivars and this market has seen little penetration from the Queensland industry.

While the Bundaberg region is currently a minor production area , the crop is relatively new to the area and interest is increasing. The region has been identified as having the best prospects for expansion with a potential production period of some 42-44 weeks (McMahon, 1991). This would be dependent upon suitable tropical hybrids being available to complement the production period for temperate hybrids.

In order to assist in the development of the fresh sweet corn industry, it became obvious that a broader range of sweet corn germplasm needed to be developed and introduced to the industry. Some new hybrids were slowly becoming available from other seed companies with United States contacts. While Australian Quarantine laws prevent direct importation of United States hybrids into Australia, a staging process via New Zealand has allowed the importation of some United States temperate hybrids. Further development of the tropical germplasm from the Kairi program for inclusion of the desirable traits required for fresh market sweet corn such as more attractive cob appearance and improved eating quality was identified as being necessary for this tropical material to be widely accepted on the fresh market.

It was for these reasons that VG436 was developed to support the joint breeding project VG319 between Queensland Department of Primary Industries and Pacific Seeds. Evaluating material produced from this breeding program was to ensure a market driven focus for the fresh market. Comparative evaluation of the Kairi germplasm and commercial hybrids from all other available sources formed an integral part of this project. This report documents the progress made by VG436 over its 3 year duration.

4

2. MATERIALS AND METHODS

The project was strongly field oriented with field studies being conducted at four locations:-

2.1 Kairi

The original sweet corn populations from Hawaii which contained the normal or sugary (su) sweet corn gene were crossed with sources of the supersweet mutant genes, shrunken-2 (sh2) and brittle-1 (btl). Development of this material and production of all subsequent tropical hybrids was undertaken at Kairi Research Station as well as some evaluations for cob quality and leaf disease resistance. The major emphasis of the Kairi program was to develop tropical hybrids This component was carried out by Ian Martin and Terry McCarthy.

The first series of tropical sh2 and btl hybrids were produced during 1994-95 for evaluation in the major growing areas. A second series of sh2 hybrids was generated in the winter of 1995 and screened at Kairi in autumn 1996,as well as at the other sites. A further group generated in 1996 were assessed at Kairi in autumn 1997. These screening trials supplemented the assessments made at Gatton. Emphasis was placed on identifying hybrids with good agronomic and quality attributes suited to fresh market production in the major sweet corn growing areas of the State. Hybrids were rated using a modified evaluation system adapted from a system used by the Crookham Seed Co. in the U.S.A. and Snowy River Seeds in Australia, the same system being used for evaluations in the other screening trials at Gatton and Bowen. Plant characteristics such as resistance to Turcicum leaf blight and common rust, seedling vigour, freedom from lodging and cob attributes such as husk cover, husk colour, cob appearance, kernel colour, pericarp (kernel) tenderness, flavour and sweetness were the major characters rated in the Kairi screening trials.

2.2 Gatton

Pacific Seeds research farm was used for the production of tropical x temperate hybrids from elite tropical inbreds and available temperate inbreds. The introduction of temperate inbreds was to improve the appearance and cob quality aspects of the tropical material while maintaining its excellent disease resistance. This site was also used for the evaluation of new tropical hybrids from the Kairi program and the more promising new temperate hybrids identified in the Bowen program. This work was conducted by the Pacific Seeds staff of Errol Corsan and Graham Schull.

Hybrid Evaluation Trials

A diverse range of hybrids generated at Kairi and Gatton were screened in three trials over spring, summer and autumn during 1994-95 for yield, disease tolerance and quality determination for the fresh market. Some forty tropical, twenty-two temperate x tropical and seven standard commercial temperate hybrids were evaluated in this series of trials. The results of field trials to date, the direction and future outcomes of the project and issues dealing with pest control and market preference perceptions were presented to growers and associated agribusiness participants at a field day at Pacific Seeds research farm in February 1995.

5

Over the 1995-96 season, three trials were conducted in spring in which commercial temperate hybrids, temperate x tropical crosses, tropical hybrids, commercial temperate bicolours and temperate x tropical bicolours were assessed. In all, some seventy hybrids were screened in these trials for yield and quality parameters. A further sowing in autumn assessed new temperate x tropical and tropical hybrids against commercial temperates in three separate trials. Some two hundred and fifty new hybrids were assessed in these plantings.

During the 1996-97 season, new material for the Spring '96 trial was limited to only four new temperate x tropical yellow hybrids and one bicolour. In the autumn '97 trial, two hundred and forty-three early generation and twelve advanced temperate x tropical hybrids and sixty-eight new tropical hybrids were assessed. In addition to these shrunken-2 hybrids, twenty supersweet hybrids containing the brittle-1 (btl) gene for sweetness from the Kairi program were evaluated. The single most promising of the more recent tropical hybrids and the best temperate x tropical hybrid from the Kairi and Gatton breeding programs were field tested on a major growers property in early 1997 in a preliminary step prior to a possible release of these two hybrids.

Virus Screening

Screening for resistance to diseases, particularly JGMV, of all tropical hybrids produced at Kairi and tropical x temperate hybrids produced at Gatton was also carried out at Pacific Seeds farm at Gatton. These assessments were conducted by Denis Persley.

During the autumn of 1995 twenty-seven tropical hybrids, twenty-two tropical inbreds and three commercial temperate hybrids were screened for resistance to JGMV. The level of JGMV was increased by planting spreader rows of susceptible grain sorghum several weeks before planting the trial. The trial entries were exposed to natural infection by aphid vectors and were rated for numbers of plants with symptoms and symptom severity, fifty-five days after planting. Disease pressure from JGMV was slight in the Lockyer Valley in autumn 1996 and reliable assessments of virus resistance could not be made. In autumn 1997, a further screening of breeding lines and hybrids was undertaken. One hundred and sixty-five second generation (S2) and nineteen third generation (S3) inbred tropical lines along with tropical, temperate x tropical and temperate hybrids were screened. Sorghum spreader rows were again used and trial entries were exposed to natural inoculation by aphids.

2.3 Bowen

Screening trials of a wide range of new temperate hybrids from all available commercial sources were conducted at Bowen Horticultural Research Station. Detailed assessments using the evaluation criteria referred to earlier were conducted for the Bowen trials. Seed for these trials were supplied by the following :-

Snowy River Seeds S & G Sandoz Seeds Henderson Seeds Yates Vegetable Seeds Pacific Seeds New World Seeds (now Yates) Macquarie Valley Seed Co.

6

Some tropical germplasm was also represented in a limited number of hybrids from Macquarie Valley Seed Co. and Yates Vegetable Seeds.

The more promising tropical sh2 and btl hybrids generated at Kairi and identified in screening trials at Gatton and Kairi were also assessed for their fresh market suitability at Bowen.. Evaluations of the better tropical x temperate hybrids from the Gatton program were also included in the Bowen screening trials. Assessments at Bowen were mainly of a qualitative nature. Emphasis was placed on identifying those hybrids with the best agronomic characters and superior cob quality attributes, with limited yield testing being carried out. Field plots were 10m. long, either four row or two row and one or two replicates, depending on the availability of seed.

During the 1994-95 season two field trials were conducted in late 1994 at Bowen Horticultural Research Station. The first trial involved screening four tropical hybrids from the Kairi program and ten new temperate hybrids from Snowy River Seeds against ten commercial temperate hybrids which included the major temperate cultivar grown in Queensland, Goldensweet. This trial became the central focus of a sweet corn field day held in early November, 1994. The second trial was a yield trial comparing five tropical hybrids with three temperate commercial cultivars. A trial in early 1995 involved evaluation of eleven supersweets containing the btl gene for sweetness, grown at a distance from other sweet corn containing the sh2 gene. In a second trial, twenty-three of the more promising tropical hybrids from the summer 1994-95 screening at Gatton were assessed against the main commercial temperate cultivars.

Three plantings in 1995-96 evaluated the more promising new temperate hybrids identified from the 1994-95 trials compared with commercial temperate cultivars, a range of new temperate hybrids from Henderson Seeds, Snowy River Seeds and New World Seeds (now Yates) and temperate x tropical hybrids from Macquarie Valley Seed Co. and Pacific Seeds.

During 1996-97, twenty-five of the better tropical hybrids from the earlier screening at Gatton were evaluated in a July 1996 sowing. Emphasis was placed on identifying those hybrids with good plant characteristics and superior cob quality attributes. A repeat of the earlier trial involving all the available commercial seed company material was sown in early August 1996, and was used as the central focus for a field day in late October. Two trials were conducted in the first half of 1997. The first trial sown in May assessed new experimental temperate hybrids from Snowy River Seeds against the best of the tropical hybrids and commercial temperate cultivars. In the second trial sown in mid June, the best of the temperate x tropical hybrids from the Gatton program, some new hybrids via Yates Vegetable Seeds and a range of commercial temperate hybrids were evaluated.

2.4 Bundaberg

The cultivars used in earlier evaluations at Bundaberg ( Olsen et al, 1990) have been superseded, while sh2 tropical cultivars were not available at that time. A new range of superior temperate hybrids has become available and performance data on these and tropical hybrids is necessary to determine optimum production periods for the newer sh2 sweetcorn hybrids at Bundaberg.

In 1994-95, six plantings were made at 2-monthly intervals over a twelve month period.

7

Planting times were mid-September, mid-November, mid-January, mid-March, mid-May and mid-July. Harvest times were late November to mid-December, mid-January to early February, early to mid-April, June, September and mid-October to early November respectively. In these plantings, the tropical cultivars H5, H13, H15, H43 and H44 were compared with the temperate cultivars, Challenger, Florida Supersweet and Goldensweet.

During 1995-96 and early 1996-97, H5 was compared with the temperate cultivars, Challenger, Punchline, Krispy King, Goldensweet, Finale, Gladiator and Florida Staysweet over the same period as described for 1994-95. Plant population was 40,000 plants per hectare in 1994-95 and 55,000 plants per hectare in 1995-96. One further trial in late 1996-97 compared the best of the tropical cultivars so far identified, H5, H44 and H141 with the temperate cultivars Gladiator, Mecca, Headstart, Goldensweet. and the best of the temperate x tropical cultivars so far identified, Pac 377.

Cobs were harvested at 76.0% moisture content. Yield was divided into A, B and C grade cobs. A grade could be sold fresh in husk. There was less than 2cm of unfilled cob, no Heliothis damage and no other defects, such as blanking (missing kernels). B grade consisted of cobs with more than 12cm of useable cob. B grade cobs resulted from tip fill problems, Heliothis damage and moderate blanking and could be sold in pre-packs. C grade cobs had less than 12cm of useable cob and were classed as rejects. Other measurements taken were plant height, plant height to main cob, total soluble solids of kernel pulp, number of rows of kernels and kernel depth. Results for some of the parameters are not presented in this report.

3. RESULTS

3.1 Kairi

One hundred sh2 tropical hybrids were assessed in 1995-1996 as an adjunct to the evaluations in the major fresh market sweet corn production areas of Bowen-Burdekin and the Lockyer Valley. Ratings for some of the more important cob quality attributes of the better hybrids identified in this screening are shown in Table 1.

Table 1. Cob Quality Ratings for Tropical Sweet Corn Hybrids

at Kairi, May 1996

Jhbrid Tenderness Ma vim r Kernel Colour

H141 6.50 5.60 5.52 H142 6.00 7.11 5.99 H152 6.00 4.93 5.52 H44 4.50 6.55 6.50 H5 4.00 5.16 5.48 LSD 5% 1.46 1.67 1.32 Ratings -1 = poorest, 9 = best

The significant improvement in pericarp tenderness as demonstrated by H141 over the hybrids already released from the breeding program, H5 and H44, is a welcome addition to the quality attributes required for the fresh market.

In 1996-97, some sixty-eight sh2 tropical hybrids were screened at Kairi. These included several of the better hybrids so far identified as well as many new hybrids. Cob quality attributes for a range of hybrids from this evaluation are displayed in Table 2.

Table 2. Cob Quality Ratings for Tropical Sweet Corn Hybrids

at Kairi, May 1997

Hvbrid 1 endcrnt'ss Ha\our kernel Colour

H229 6.33 7.06 4.81

H217 5.75 6.05 5.40

H231 5.70 6.20 5.70

H141 5.65 6.20 5.85

H191 5.00 5.60 5.05

H212 4.95 5.65 6.25

H5 4.70 5.05 5.10

H184 4.37 6.34 5.59

H13 3.80 5.00 5.10

LSD 5% 0.995 1.07 1.40

Ratings -1 = poorest 9 = best

H141 has again shown a significant improvement in tenderness over H5, the only tropical hybrid so far to be used as a fresh market cultivar. The new hybrids H229, H217 and H231 also rated well in these quality assessments

3.2 Gatton

Hybrid Evaluation Trials.

In 1994-95 a number of tropical hybrids rated higher in several attributes than H5. Several of the temperate x tropical hybrids also performed well, particularly in terms of kernel flavour and colour and virus resistance. Table 3 demonstrates the advantages the tropical and temperate x tropical material has over the temperate material when virus pressure is high, as occurred in the autumn trial of 1995.

Table 3.

9

Sweet Corn Hybrid Evaluations Gatton, May 1995

Hybrid Tjpc Murki'lahle ^ icld L'hu

disease resistance. They also suggested improvements in emergence, seedling vigour and earlier maturing types to allow for 'catching up' when weather conditions were adverse.

In the 1995-96 spring trials, disease pressure from JGMV was slight in the district which allowed a good comparison between the temperate and tropical material. The virus was more prevalent later in the season. Of the tropical hybrids, H44, H45, H48 and H67 again performed well, yielding 23.lt/ha, 24.lt/ha, 24.5t/ha and 24.9t/ha respectively, outyielding H5 at 21.4t/ha. The commercial temperate cultivars were lower yielding than the tropicals, with yields ranging from 8.3t/ha for Honeysweet to 16.lt/ha for Finale, the experimental hybrid from Snowy River Seeds. The major commercial cultivar Goldensweet and the newly released Gladiator (both Snowy River Seeds) produced intermediate yields of 13.0t/ha and 14.0t/ha respectively. The best of the temperate x tropical yellow hybrids produced yields intermediate between the parental types, while the promising temperate x tropical bicolour outyielded all the commercial temperate bicolours. Some comparative measurements on a range of the various hybrids tested are shown in Table 4.

The tropical hybrids were later maturing and phenotypically taller statured with cobs held higher on the plant than the temperate hybrids. The temperate x tropical hybrids tended to be intermediate in these characters although some variation existed. In the autumn trials sown in February 1996, the temperate cultivars were severely affected by JGMV, although the virus pressure was generally lighter in the Lockyer Valley at the time of planting. Plants were stunted, slow to mature and produced relatively low yields ( Challenger - 4.6t/ha, Krispy King - 0.4t/ha, Goldensweet - 5.4t/ha, Gladiator - 1 l.lt/ha, Finale - 12.2t/ha and Florida Staysweet - 9.7t/ha compared to H5 -24.0t/ha and H44 - 22.7t/ha.

Cob husk leaves were also stunted allowing water to enter cobs, resulting in cob fermentation. In contrast, the tropical and temperate x tropical hybrids withstood the effects of the virus. Two of the new hybrids tested showed promise for use as fresh market cultivars. H141, a tropical hybrid, yielded well (22.lt/ha) in comparison with H5 (24.0t/ha) and also possessed a pericarp softness and flavour comparable to some of the best temperate commercial hybrids. A promising new temperate x tropical hybrid, 61418, produced equivalent yields to H5 and was also rated as being a contender for commercial fresh market production. This hybrid, now identified as Pac 377, performed well in most of the cursory attributes such as appearance, flavour, texture, kernel colour, but was ranked only slightly softer in pericarp toughness than H5.

In the 1996-97 season, disease pressure from JGMV was moderate to severe through the Lockyer Valley. Consequently, the commercial temperate cultivars suffered both yield and quality losses while the tropical hybrids tested recorded a nil level of virus. Of the temperate cultivars, only Gladiator and Punchline showed any virus tolerance with yields of 13.2 and 12.lt/ha respectively, compared with Finale 9.7t/ha; Krispy King 8.4t/ha; Headstart 6.1t/ha and Goldensweet 2.7t/ha. Of the tropical hybrids, H5 produced the highest yield of 29.6t/ha while the promising temperate x tropical hybrid, Pac 377, yielded 21.2t/ha. This was a new version of Pac 377 which maintained the favourable quality aspects of the previous version but with an improvement in pericarp tenderness.

With the brittle hybrids, the overall quality was poor. Plants were lacking in uniformity and all but four of the twenty hybrids tested had red tassels and red silks, an attribute which is

11

http://23.lt/hahttp://24.lt/hahttp://16.lt/hahttp://22.lt/hahttp://12.lt/ha

Table 4. Sweet Corn Hybrid Evaluations

Gatton, November - December 1995

Ihbrid l \pe Marketable Yield t/ha

Days to Malurif}

Plant Heiylii

(in)

Cob Height

(in)

Honeysweet Temperate 8.3 74 1.09 0.22

Punchline Temperate 13.5 79 1.00 0.43

Challenger Temperate 12.8 80 .094 0.32

Krispy King Temperate 1.0 80 1.11 0.37

Finale Temperate 16.1 86 1.19 0.45

Gladiator Temperate 14.0 86 1.28 0.43

Goldensweet Temperate 13.0 86 .097 0.50

Florida Staysweet Temperate 12.5 86 1.24 0.49

25 140 Temp x Tropical 17.8 92 1.95 0.54

25 148 Temp x Tropical 18.8 98 1.87 0.93

H5 Tropical 21.4 95 1.83 0.88

H44 Tropical 23.1 95 1.99 0.88

H45 Tropical 24.1 95 1.67 0.98

H48 Tropical 24.5 94 1.61 0.82

H67 Tropical 24.9 95 1.01 0.82

Snogold Temp Bicolour 14.9 81 0.99 0.35

BSS4498 Temp Bicolour 16.8 85 1.12 0.37

Cabaret Temp Bicolour 16.9 85 1.24 0.49

Samurai Temp Bicolour 10.6 86 1.03 0.46

DK-5 Temp Bicolour 16.7 88 1.43 0.47

25149 Temp x Tropical

Bicolour

25.2 88 0.68

unacceptable in fresh market sweet corn. They also rated poorly in terms of quality attributes such as kernel colour, flavour, texture and pericarp tenderness, although there was some variability in these characteristics. In the semi-commercial field testing of H141 and Pac 377 in a growers field, H141 matured around one week earlier than H5 and appeared to be less daylength sensitive. The grower

12

reported less pollination problems and improved eating quality over H5. Pac 377 also performed well and may become a useful cultivar with slightly more refinement.

Virus Testing

In the autumn 1995 trial, all of the sh2 hybrids from Kairi, with the exception of H57,had adequate JGMV resistance (0-25%; mean 8%). The disease pressure in the trial was very high and was greater than that usually found under commercial conditions. In general, hybrids and inbreds with a high incidence of JGMV developed severe symptoms while those having resistance to infection also developed mild to intermediate symptoms.

Virus spread in the autumn 1997 trial was slow during the early stages and disease levels somewhat uneven over the two replicates. However final disease levels were adequate to allow a satisfactory screening of entries. A summary of the trial data is given in table 5.

Table 5 Screening of Lines and Hybrids for Resistance to JGMV

Gatton, February - March 1997

Entry Sweet Corn Type j JGMV %

S2 lines Tropical inbred 20 S3 lines Tropical inbred 7 Line 17 Tropical inbred 34 Line 3 Tropical inbred 0

Line 56 Tropical inbred 0 H5 Tropical hybrid 0

H141 Tropical hybrid 0 H44 Tropical hybrid 0

Florida Staysweet Temperate hybrid 25 DK5 Temperate hybrid 35

Finale Temperate hybrid 52 Jubilee Temperate hybrid 71

mini Gold Temperate hybrid 41 Samurai Temperate hybrid bicolour 59

Golden Pearl Temperate hybrid bicolour 29 Pac 377 Temperate x Tropical hybrid 20 Pac 379 Temperate x Tropical hybrid

bicolour 5

Pac 412 Temperate x Tropical hybrid 3 Pac 406 Temperate x Tropical hybrid 59

3.3 Bowen

The first hybrid evaluation trial in the 1994-95 season was sown in mid August and matured in early November. A very successful field day was held at Bowen Horticultural Research

13

Station centred around this major cultivar evaluation. The field day was very well attended by sweet corn growers in the Bowen-Burdekin region as well as major growers from Southern Queensland, seed company representatives from local and interstate, and members of the project team.

Of the twenty-four supersweet hybrids evaluated, the major commercial standard, Goldensweet, produced the best overall quality cobs, although husk cover and plant style could be improved. The commercial cultivar Florida Staysweet produced reasonable quality cobs but was very susceptible to common rust Puccinia sorghi. However, the superior husk cover of this cultivar is an attribute which may give it some protection against heliothis (corn ear worm) Helicoverpa armigera.

In conjunction with all participants, a number of new temperate supersweet hybrids were identified for their commercial potential for the fresh market. The best of these were Krispy King, Headstart, Gladiator and Finale. A number of bicolours were also included, the best of these being Golden Pearl, an established cultivar which has been exported on occasions from Southern Australia. The bicolour BSS4498 also deserved some consideration. The industry members at the field day commented on the need for a wider range of varieties, the industry in North Queensland being heavily dependant on one variety. They also remarked on the need for varieties with good turcicum leaf blight resistance, better emergence and seedling vigour, and some good quality earlier maturing types. Heliothis management was also a constant issue.

The tropical hybrids were less favoured by growers in the dry tropics for the fresh market, since JGMV resistance is of minor interest in this region. However, some growers favour these for late season plantings, and H5 was the most favoured of the tropicals with H44 also of interest because of its better uniformity.

In the second trial also sown in mid-August, the temperate hybrids produced some useable second cobs while the tropicals generally did not develop useable second cobs. Cob maturity was more uniform with H44 than with the other tropicals in the trial, while the temperates were all quite uniform in maturity. Results are shown in Table 6.

H15 and Goldensweet produced significantly higher yields of cobs than H5, H13 and H43. The temperate hybrids also produced more useable cobs than H5. With the exception of HI 3, cob size of the tropical hybrids was generally larger than the temperate hybrids. Of the tropical hybrids, H44 produced cobs with the best uniformity and eating quality closest to that of H5

In the trial in early 1995 to evaluate the brittle lines, these hybrids displayed better tip fill and cob shape than the sh2 tropical hybrids. Cob shape of the btl hybrids was more cylindrical, with some hybrids having excellent tip fill. The brittles generally possessed a tough pericarp, although bt26 and bt27 were noticeably more tender than the rest. Most lines had good tight husk covers which extended beyond the cob tip, with the exception of bt7 which had some ears extending beyond the husk. A common fault with all the brittles was the range in kernel colour at maturity, with a mixture of lemon, yellow and pinkish tinged kernels. Variability within hybrids for maturity, row straightness, tip fill and kernel blanking on cobs also occurred. Sweetness was generally acceptable for the brittles while flavour and texture were more variable. Overall, the best of the brittle lines were bt8 and bt28.

14

Table 6 Sweet Corn Yield Trial - Bowen, November 1994

Total ( \ grade + It grade) Cullivar lhns to

silk

Da\s to har\ est

Plant height

cm.

Cob height

cm.

Cob No.

Cob Wt.

+ husk

Cob Wt.

- husk Cob

Size i».

H5 63 86 297 131 15.6 7384 4520 288.3 H13 62 84 258 120 16.6 6205 4234 254.3 H15 63 86 297 110 19.6 9407 5778 293.9 H43 62 86 275 119 15.6 7164 4381 279.9 H44 62 86 272 117 18.3 8690 5269 287.5 Challenger 49 71 170 49 20.6 7342 5260 254.7 Golden Sweet

56 78 240 55 23.0 9799 5742 248.8

Florida Supersweet

58 80 223 77 21.3 7335 4700 220.0

LSD (P=0.005)

4.2 1698 1145 30.9

The tropical hybrids assessed in mid 1995 produced longer, slimmer cobs which tended to taper towards the tip when compared with the temperate hybrids against which they were assessed. They were also taller plants and later maturing. The best of the tropical hybrids were H5, H44, H45, H49 and H61, all of which matured about ten days later than Goldensweet.

In the first of the 1995-96 trials, three new temperate hybrids from Snowy River Seeds, Gladiator, Supersweet Yellow and Finale were evaluated against Florida Staysweet, Goldensweet, Krispy King and Challenger in late 1995. Gladiator was the choice of the newer hybrids having vigorous uniform plants, good plant characteristics, large cob size (around 400g in husk) and good husk cover. However, this cultivar has paler kernels and slightly tougher pericarp than Goldensweet and a tendency for cobs to hang out from the plant, sometimes becoming damaged during harvesting. Supersweet Yellow and Finale were of poor seed quality, low vigour, and only average cob quality. These cultivars have not become commercial. In 1996, fourteen hybrids were screened in a May sowing which included commercial

temperate hybrids previously evaluated, two new temperate hybrids 8198 and 76BB80D and two temperate x tropical hybrids Pac 383 and Pac 379, a bicolour. Pac 383 produced small cobs with good husk cover, good kernel colour and tip fill and reasonable eating quality, but uneven jumbled rows on all cobs detracted from its appearance. Pac 379 had quite a tough pericarp but overall was quite reasonable and appears to have good yield potential. 76BB80D had poor tip fill, average kernel colour and slightly tough pericarp. Overall, it showed little promise. 8179 was of similar plant style and cob type to Gladiator but with a tougher pericarp. Overall, the best quality cobs were produced by Goldensweet, with

15

Gladiator being disappointing in this screening trial producing tapering cobs with poor tip fill. Gladiator appears to be more suited to early and late season production.

In the last of the 1995-96 evaluations, thirty-five hybrids including the standard commercial temperate cultivars were screened in a late June 1996 sowing. Following 12mm. of rain and strong wind, a number of lines lodged severely, the worst being S905A, Mini Gold and S906A (Hendersons), Samurai and Golden Pearl (Snowy River), Exp.5 and Exp.6 (Macquarie Valley). The Henderson lines were generally quite variable within each hybrid, having poor quality cobs with jumbled rows, shallow kernel depth and average to poor eating quality. None of these lines were commercially acceptable. The Macquarie Valley hybrids were also variable with medium to large cobs, some quite tough, with all showing tip blanking. These hybrids appeared to have tropical germplasm background.. None were developed sufficiently to be of commercial use.

Of the PAC seed lines, the 60000 series of tropical x temperate hybrids were generally strong erect plants with little or no lodging and with some tendency to tiller. However cob quality suffered generally with poor tip fill, toughness, and poor flavour and sweetness. The best of these lines in this planting were 60029 and 60189 which had better tip fill and softer pericarp. PAC 377 was also of reasonable quality as was the bicolour PAC379.

Punchline and Cabaret (bicolour) from Yates produced good quality cobs although Punchline tends to be too small for market requirements. The Snowy River lines Gladiator and Headstart were overall the best of the newer hybrids tested. Gladiator produced better quality cobs than in the earlier trial and appears to be more robust and reliable than Goldensweet. However it suffers from the disadvantage of paler kernel colour and a large proportion of cobs are too large for the market requirements. Headstart produced cobs of similar quality to those of Goldensweet, but with a better husk cover. The main disadvantage with this variety are its lack of resistance to rust and turcicum leaf blight.

In the first of the 1996-97 evaluations, of twenty-five tropical hybrids screened eight hybrids rated higher for the sum total of the quality attributes of flavour, tenderness, cob appearance and kernel colour than H5 and H44, although differences were not statistically significant. The most promising hybrid for fresh market use was H141 which was significantly better than H5 and H44 in the quality attributes of flavour and tenderness and equal in kernel colour. Results for the best ten hybrids are shown in Table 7.

Table 7 Quality Characteristics of Tropical Supersweets

Bowen, October 1996

Hybrid Flavour 7.50

Tenderness Cob Appearance Kernel Colour Total H141

Flavour 7.50 6.50 6.50 6.00 26.50

H147 6.00 6.50 7.00 6.50 26.00 H101 6.64 5.84 5.09 7.07 24.64 H122 6.00 6.00 7.00 5.50 24.50

16

H143 6.00 5.00 7.00 6.00 24.00 H132 6.50 4.50 6.50 6.50 24.00 H152 6.00 7.00 5.50 5.00 23.50 H163 7.36 4.16 6.91 4.93 23.36 H5 6.00 4.00 7.00 6.00 23.00 H44 5.50 3.50 8.00 6.00 23.00 CV 10.3 21.0 16.3 15.9 9.6

LSD 5%

1.29 2.38 2.02 2.00 4.70

All ratings on 1-9 basis 9 = Best 1 = Worst

The second of the 1996-97 trials sown in early August contained most of the hybrids included in the last of the 1995-96 evaluations as well as the new temperate hybrids Mecca and Maverick. The PAC seed lines 60029 and 60189 which had previously looked promising were disappointing in this trial with long slim tapering cobs and problems with tip blanking. 60029 also had cobs protruding beyond the husk cover. PAC377 was the best of the yellow PAC seed lines. Overall, the best lines were Goldensweet, Gladiator, Headstart and Mecca which produced good quality attractive cobs.

A successful field day was held around this trial at which

• an update on the fresh market sweet corn project was provided

• project team member Terry McCarthy gave an address on his recent rip to Hawaii and the US to attend the National Sweet Corn Breeders Meeting in Oregon.

• plots of the latest hybrids from commercial breeding programs were on view.

Two trials were sown in late 1996-97, the first being sown in mid May and included the standard commercial temperate hybrids, a range of other temperate commercial varieties and the tropicals H5 and H141. Several new experimental hybrids from Snowy River were included but failed to germinate satisfactorily. Ten varieties were yield tested. Results are shown in Table 8.

Table 8 Sweet Corn Yield Trial

Bowen, May 1997

\ ariet\ Davs lo maturity

Marketable ( obs/plant Size

Goldensweet 85 1.16 298 18.6 71

H5 96 0.88 377 17.8 45

Gladiator 84 1.00 338 18.0 68

Headstart 82 1.10 299 17.5 74

Florida Staysweet 85 1.18 283 17.8 73

Punchline 77 0.95 267 13.5 63

Honeysweet 69 0.71 321 12.3 30

Mecca 82 1.05 333 18.7 47

Finale 84 1.03 269 14.8 71

The major commercial varieties Goldensweet, Gladiator, Florida Staysweet and H5 produced very acceptable marketable yields but the proportion of A grade cobs produced by H5 was unsatisfactory. Headstart also yielded well and produced an acceptable proportion of A grade cobs. H141 while lower yielding, produced a high proportion of A grade cobs. Mecca yielded well but the proportion of A grade cobs was unsatisfactory. Downgrading of cob quality generally in this trial was due to poor tip fill and blanking elsewhere on cobs.

The second trial for 1997 sown in mid June included the major commercially available temperate varieties for comparison as well as a range of new hybrids from Yates, Snowy River and Pacific Seeds. The trial block was subjected to strong wind and rain over 30-31st August following an irrigation; this resulted in lodging in all plots except the hybrids Cabaret and Punchline.

The standard commercial hybrids Goldensweet, Gladiator and Florida Staysweet performed as expected. The newer commercial hybrids {Headstart, Cabaret, Punchline, and Mecca), also performed as expected. Overall, the cobs most commercially acceptable came from Goldensweet, Headstart and Gladiator. Florida Staysweet was also acceptable but is more suited to the warmer conditions during the early part of the season. Mecca produced reasonable quality cobs but cob appearance was less attractive than the major commercial hybrids. Lodging in several trials has also been noted as a problem with this variety. Punchline again produced very good quality uniform cobs but cob size is slightly smaller than the Australian domestic market favours. Cabaret is a good quality, uniform bicolour, but the domestic market is very limited for bicolours.

The experimental hybrids from Yates Seed Company were not regarded as commercially acceptable. They were generally quite variable, off-types were present in some hybrids, and most had unattractive cob appearance or husk cover was unattractive. The best of the Pacific Seeds temperate x tropical hybrids was 70981, but it's smaller cob size, lack of flag leaf and tougher pericarp are disadvantages for commercialisation. Of the Snowy River Seeds experimental lines, 719 produced good quality cobs but lacking in size. Seed quality was also poor.

3.4 Bundaberg

18

Yield Marketable yield data (cob in husk) and A grade fresh yield data (cob in husk) for Year 1 (1994/95) are presented in Tables 9 and 10. The tropical cultivars produced consistently high marketable yields over the 6 planting times. In the January planting, yield of H5 was significantly (P0.05).The marketable yield of the temperate cultivars, Challenger, Florida Supersweet and Goldensweet, was not significantly (P>0.05) different than any of the tropical cultivars for the September, November and March plantings. H5 and H44 had significantly (P0.05) different from each other. Considering A grade fresh yield, the September planting was the only one to produce a reasonable yield over all cultivars for this category. In all other plantings, the yield of A grade fresh cobs was generally low. Goldensweet produced significantly (P

l.s.d. (P=0.05) 3.37 3.25 N.A 2.43 1.73 3.04

Marketable yield data (cob in husk) and A grade fresh yield data (cob in husk) for Year 2 (1995/96) are presented in Tables 11 and 12. In the January planting, all cultivars yielded well for marketable yield with the yield differences between cultivars not significant (P>0.05). The most reliable performers over the 6 planting times were H5, Gladiator and Goldensweet although marketable yield for the November and March plantings was reduced because of adverse weather conditions which caused poor pollination. Leaf disease was again a major problem in the temperate cultivars and reduced yield severely. There were heavy infections of common rust in Punchline, Challenger, Krispy King, Finale and Florida Staysweet while Goldensweet was severely infected by turcicum leaf blight. Ratings for these diseases are given in Table 5. Gladiator and Goldensweet were resistant to common rust while Gladiator was moderately tolerant to turcicum leaf blight. A grade fresh yield was poor for most plantings. Goldensweet showed the best potential for good quality cobs.

Table 11 Marketable yield - cob in husk (kg/plot) -1995/96

Means within columns followed by a common letter are not significantly different at P=0.05

('tilth nr I'luntinu Time ('tilth nr Sept No\ Jan Mar Mav lul

H5 15.76a 8.78a 15.94 3.21 8.82 12.00a

Punchline 2.71* 8.86a 13.39 0.00 0.30 0.1 T Krispy King 3.98et 5.75abc 13.63 0.00 0.00 4.02b

Gladiator 13.88ab 2.46c 14.70 1.36 6.60 11.40a

Finale 9.17cd 8.20a 13.08 0.08 0.00 1.64c

Challenger 6.28de 7.64ab 14.50 0.30 0.00 0.45c

Florida Staysweet 7.91d 4.36bc 13.19 0.00 0.00 0.51c

Goldensweet 11.89bc 5.69abc 12.36 0.00 7.44 11.10a

l.s.d. (P=0.05) 3.31 3.38 N.S N.A N.A 2.36

Table 12 A Grade Fresh yield - cob in husk (kg/plot) -1995/96

Means within columns followed by a common letter are not significantly different at P=0.05

(.'ulliviir Planliiii: Time (.'ulliviir Sept Nm Jan Mar Ma> Jul

H5 0.41 1.26 0.30c 0.00 0.37 4.52ab

Punchline 0.00 2.20 6.05a 0.00 0.00 0.00d

Krispy King 0.00 1.09 4.03ab 0.00 0.00 1.23cd

Gladiator 2.78 0.72 2.84bc 0.11 1.24 2.87bc

Finale 0.11 1.56 3.50ab 0.00 0.00 0.10d

Challenger 0.11 1.46 3.88ab 0.00 0.00 0.00d

Florida Staysweet 1.45 1.86 5.52a 0.00 0.00 0.17d

Goldensweet 1.70 2.02 6.08a 0.00 3.59 5.33a

l.s.d. (P=0.05) N.A N.S. 2.59 N.A N.A 1.96

20

Disease resistance

Disease is a serious problem in supersweet corn where crops are planted in close time sequence because of the inoculum build up factor. The main diseases at Bundaberg are Common rust and Turcicum leaf blight.

Table 13 Ratings for Common rust and Turcicum leaf blight on supersweet corn at Bundaberg

1995-96

(ulthar Rust

rating Turcicum

rating H5 2 3 Punchline 3 3 Krispy King 5 5 Gladiator 1 3 Finale 5 4 Challenger 5 4 Florida Staysweet 5 5 Goldensweet 1 5

l=nil, 5=severe Insect resistance

Heliothis damage at selected planting times is shown in Table 14. It appears that the level of Heliothis damage is related to the level of insect pressure at any one time. Even with constant spraying (every second day) at silking, Heliothis control is difficult. It was expected that the tropical cultivars with a tight husk cover would offer some measure of resistance but they failed under high insect pressure. Florida Staysweet seems to resist Heliothis attack to some extent. Heliothis damage was responsible for much of the downgrading of cob quality from A grade fresh to B grade cobs.

Table 14 Percentage of Heliothis damaged cobs in supersweet corn at various planting times at

Bundaberg Means within columns followed by a common letter are not significantly different at P=0.05

Cullmir lMunling Time ( tilth ar Planting Time Cullmir Sept 1994

.Ian 1995

Ma> 1995

( tilth ar Sept 1995

\ o \ 1995

.Ian 1996

H5 5.69 89.61 0.90b H5 17.71c 0.77c 76.84" H13 9.52 71.55 16.11a Punchline 89.58" 23.03" 40.59bc

H15 18.18 51.53 - Krispy King 83.09" 15.25abc 51.02b

H43 17.12 81.17 6.24b Gladiator 46.51b 10.41abc 42.86bc

H44 16.88 86.39 17.76" Finale 51.57" 5.3 lbc 35.96bc d

Challenger 25.42 82.74 1.04b Challenger 77.03" 8.89"bc 58.28ab

Fl. Supersweet 22.69 85.67 1.01b Fl. Staysweet 11.64c 17.04"b 14.62d

Goldensweet 6.57 73.12 1.01b Goldensweet 43.42b 9.49abc 20.46cd

21

l.s.d. (P=0.05) N.S. N.S. 7.47 18.09 15.29 24.13

Tip fill

This aspect causes heavy downgrading of cob quality of the tropical cultivars to B grade cobs. Data is not presented in this report.

Total Soluble Solids

Table 15 shows that there is nothing clear cut with regard to the total soluble solids content of different cultivars. At different planting times, different cultivars have the highest total soluble solids content.

Table 15 Percentage total soluble solids content of supersweet corn at different planting times

Means within columns followed by a common letter are not significantly different at P=0.05

Cultivar Planting Time ('tilth ar Planting Time Cultivar Sept 1994

Jan 1995

('tilth ar Sip! 1995

Jan 1996

H5 15.0" 15.8"e H5 18.4ab 17.0b

H13 15.1c" 16.1c" Punchline 1 ? 4 a b 17.1b

H15 15.9ab 15.6e Krispy King i i-i ^ a b 17.5b

H43 16.0a 16.4bc Gladiator 18.5a 17.3b

H44 15.8bc 16.5b Finale 1 ? 7 a b 17.2b

Challenger 15.1c" 14.6* Challenger 15.4C 16.1c

Fl. Supersweet 15.8bc 17.6a Fl. Staysweet 17.3b 15.0" Goldensweet 16.6a 16.5" Goldensweet 17.6ab 19.4a

l.s.d. (P=0.05) 0.7 0.3 l.s.d. (P=0.05) 1.1 0.5

Plant height

Total plant height and height to main cob are shown in Tables 16 and 17. The tropical cultivars, H5 and H44, had significantly (P !9«>5 i 1995

Culthiir Sept 1995

ian 1996

H5 2864a 298 la 2408a H5 2629a 2933a

H13 2429c 2494c 2110b Punchline 1707" 1790" H15 2727b 2807b - Krispy King 1703" 1783" H43 2763ab 2904a 2327a Gladiator 2114b 2252b

22

H44 2805ab 2950a 2412a Finale 1734d 1831d

Challenger 1796' 1861' 1350d Challenger 1688d 1865d

Fl. Supersweet 1978d 2203d 1625' Fl. Staysweet 1907' 2071' Goldensweet 2044d 2427' 1764' Goldensweet 2097" 2230b

l.s.d. (P=0.05) 130 87 168 l.s.d. (P=0.05) 80 103

Table 17 Height to main cob of supersweet corn at different planting times

Means within columns followed by a common letter are not significantly different at P=0.05

Culli\ur Planting rime t'ulti\ar I'lunling 1 line

Culli\ur

Sepl | Jan IM«M , 1W5

\la> IW5

t'ulti\ar

Sent IW5

Jan 1M96

H5 1113a 1195a 986a H5 1071a 1095 a

H13 1009b 1015' 934a Punchline 500cd 644cd

H15 1047ab 1075bc - Krispy King 448d 460g

H43 1071ab 1130b 1029a Gladiator 643b 673' H44 1088ab 1215a 1015a Finale 540' 580e

Challenger 501d 4881 285' Challenger 483d 531* Fl. Supersweet 701' 816d 499b Fl. Staysweet 659b 725b

Goldensweet 623' 650e 481b Goldensweet 624b 612d

l.s.d. (P=0.05) 100 62 119 l.s.d. (P=0.05) 53 44

In the final trial sown in April 1997, marketable yields were similar for Mecca (16.6t/ha), Goldensweet (15.6t/ha), H5 (14.3t/ha), Gladiator (14.2t/ha), H141 (14.lt/ha), lowest for Pac377 (11.6t/ha) and intermediate for Headstart (13.lt/ha) and H44 (12.8t/ha). Percentage of 'A' grade cobs was highest for Goldensweet (52%), Gladiator (46%), H141 (43%) and lowest for Pac377 (6%) and H44 (0%). 4. Discussion

4.1 Kairi Emphasis at the Kairi site has been on improvements to the tropical material which is generally viewed as being less desirable for fresh market production, due to the tougher pericarp and lack of flag leaf on the husk. However, the production and screening of new hybrids resulted in the release to industry of H5 and the identification of H141 as having superior eating quality to H5 for fresh market and even superior disease resistance to H5. Newer tropical hybrids also identified as having better fresh market attributes than much of the tropical germplasm, in terms of softer kernels and improved flavour, were H229, H217 and H23L

4.2 Gatton

A feature of the Gatton trials was the excellent resistance to JGMV displayed by many of the tropical and tropical x temperate hybrids, compared to the range of commercially available temperate material. While the temperate material performs well in the spring to early summer in the Gatton region, the mid summer to autumn period experiences a build-up in the level of

23

http://14.lt/hahttp://13.lt/ha

virus in the area, rendering the existing temperate hybrids less useful despite their more acceptable fresh market quality attributes. Many of the commercial temperate hybrids produced no marketable yields under heavy virus pressure and low yields under moderate pressure. Evaluations at Gatton of H141 further confirmed its better fresh market quality attributes and improved disease resistance. The temperate x tropical experimental hybrid, Pac377, also performed well at Gatton. Its superior yielding ability over the temperate hybrids was demonstrated by producing at least twice the yield of the commercial temperates under moderate JGMV pressure. While this hybrid has a lower level of virus resistance than the better tropical hybrids, its field performance is equivalent to that of H5. Should a commercial testing phase for this hybrid prove satisfactory, its release to industry will provide an addition to the range of varieties available to Queensland producers.

Further improvements in the characteristics of eating quality, cob appearance, earlier maturity and disease resistance should be assured in future hybrids. This should occur as the elite tropical inbreds used in the production of hybrids such as H141 are used in combination with temperate germplasm to produce superior quality tropical x temperate hybrids.

4.3 Bowen

The Bowen site was very useful for benchmarking of new commercially available experimental hybrids against the industry standards.. Close cooperation from the seed industry allowed these comparison trials to occur and were well appreciated by growers, being able to view the latest hybrids from all available sources in Australia at the same site.

The relatively dry climatic conditions experienced throughout the project resulted in low pressure from the major leaf diseases, common rust and leaf blight. Occurrence of JGMV in the dry tropics is also low and only minor evidence of this disease was observed through the life of the project. Pest pressure from corn ear worm varied seasonally through the region but was always a major production issue and raised by growers continually at field days and meetings.

Despite the low leaf disease pressure experienced, growers indicated severe problems have been experienced in past seasons and the lack of resistance to leaf blight in the major industry standard, Goldensweet, was of concern. Use of the older standard, Florida Staysweet, was limited to early season production due to its lack of resistance to common rust. Its tighter husk cover however was perceived to afford some protection from insect attack during the warm early season period when corn ear worm pressure was high.

Over the term of the project approximately one hundred and twenty experimental hybrids, mostly temperate and tropical and a small number of tropical x temperate lines, were benchmarked against the industry standards. The tropical hybrids were of less interest to the local industry since JGMV was not an issue and the tropicals were seen as being of inferior quality to the temperates for the fresh market. Nontheless, some interest in H5 prevailed and small areas were grown during high insect pressure periods due to its superior husk protection. H141, evaluated over the latter period of the project, demonstrated that substantial improvements in eating quality were possible within the available pool of tropical germplasm. The tropical x temperate experimental hybrid Pac377 showed some promise but quality attributes were still inferior to temperate hybrids. The better quality tropical inbreds

24

in combination with suitable temperate inbreds have the potential for major gains in the future.

The new temperate hybrid Gladiator was the most reliable and robust of the new hybrids tested and. was identified by all stakeholders as a worthwhile complement to Goldensweet, particularly during the warmer periods of the season. Its improved disease resistance and better husk protection are advantages over Goldensweet, although kernel colour is less desirable. By the end of the project, this hybrid had become established in commercial production. Other hybrids identified with commercial potential were Headstart, Krispy King and Mecca. Headstart, with the advantages over Goldensweet of earlier maturity and imroved husk protection, is disadvantaged however by its known lack of genetic resistance to common rust and leaf blight. Lack of disease resistance, low cob height for mechanised harvesting and reliable seed quality have also prejudiced the commercial acceptance of Krispy King, while susceptibility to lodging has affected the acceptance of Mecca.

4.3 Bundaberg

The Bundaberg district has the potential for almost year round production of supersweet corn. Cultivars recommended include H5, H44, Gladiator and Goldensweet. The tropical cultivar, H5, produced good yields over most plantings during the 2- year period. It has good resistance to rust and tolerance to turcicum leaf blight. Tip fill is a major problem. The majority of cobs would require trimming. H5 has a tough pericarp which may reduce consumer appeal for fresh market. H44 is also a tropical cultivar which has similar parentage and similar characteristics to H5. The temperate cultivars, Gladiator and Goldensweet, have very nice cob style with good tip fill. Low yield occurred in the March and May plantings in both years and in the November planting in year 2. The result for March was unexpected. However, during silking in year 2 we experienced windy showery weather which affected all cultivars. Goldensweet had severe turcicum leaf blight in both years' March planting which reduced yield. Gladiator has good rust resistance and tolerance to turcicum leaf blight. Goldensweet has good rust resistance but is highly susceptible to turcicum. Turcicum is a major problem during showery weather. If the crop is infected early in its growth, severe yield reduction occurs. The other temperate cultivars are highly susceptible to common rust which resulted in low yields during many of the plantings. As common rust is a major problem in this district, particularly in a sequential planting situation, they have limited potential. Since most seed companies in the United States have incorporated the gene Rpld for rust resistance into at least one elite inbred (Pataky and Mosely, 1995), newer imported germplasm from the U.S. should carry resistance to this disease.

Heliothis is a major insect problem of supersweet corn in the Bundaberg district. Even with a frequent spray program, we experienced high infestation rates with 70% to 80% of cobs affected at certain times of the year. Damage was mainly limited to the cob tip and this could be trimmed off making most cobs marketable.

4.4 Extension /Adoption by Industry

The range of new tropical hybrids produced from the breeding program at Kairi has demonstrated that superior eating quality material is available within the tropical germplasm. The high level of disease resistance in this material is borne out by the results at Gatton. The identification of the greatly improved eating quality and disease resistance in H141 is very

25

encouraging for future breeding efforts which can be expected to produce superior hybrids, particularly when used in combination with elite temperate inbreds.

New temperate inbreds have also been identified. This should help to provide greater stability to the industry by reducing the heavy reliance on one or two hybrids which don't cover the range of required disease resistance as well as having the desirable fresh market attributes. The rapid adoption of Gladiator from Snowy River Seeds as an addition to complement Goldensweet in fresh market production demonstrates the industry's need for new hybrids bred for local adaptation. Other production issues, particularly that of improved management of corn ear worm and reliable seedling emergence are other issues identified by industry participants.

It is anticipated that improved hybrids from the QDPI/Pacific Seeds temperate x tropical program should become available for testing in 1999-2000. Adoption by industry of hybrids from this and other sweet corn breeding efforts in Australia should then provide the springboard for further industry development. While industry members have expressed the desire to more rapidly access overseas varieties (as was strongly expressed at a Sweet Corn Industry Workshop at Knoxfield , March 1997), this needs to be tempered against the risk of introduction of exotic diseases which may impact upon the long-term interests of the industry

4.4 Directions for Future Research

Breeding/Cultivar Testing. A continuation of the breeding effort of transferring the excellent disease resistance of the tropical material into elite temperate germplasm to produce high quality and disease resistant hybrids with the desirable fresh market traits is essential for the longer term stability of the industry. Identification of sources of material with adaptability to the Queensland climatic environments will also enhance the local breeding effort by identifying complementary or superior germplasm. The fresh market sweet corn development is continuing from July 1997 under the project 'Breeding for sweetness and tenderness in tropical sweet corn'(Vg606).

Heliothis Management. Reducing the damage caused by heliothis in sweet corn through a better understanding of how to manage this insect is a vital ingredient in the long term viability of the industry. This could be accompanied by breeding efforts to further reduce the effects of the insect. The combined effects should reduce the heavy dependence the industry has on insecticidal use, particularly in the tropical Queensland. A proposed national sweet corn pest management project should go a long way towards achieving this industry objective.

Plant Establishment. Agronomic or breeding efforts to improve the emergence and vigour of supersweet cultivars, particularly where soil conditions are less than ideal, have been raised by industry members on numerous occasions. Investigations into seed treatments, soil environment etc may yield some answers.

4.5 Financial Commercial Benefits

By improving yields and quality and expanding the harvesting season through the use of better adapted cultivars, economy of growing and marketing are seen as commercial industry

26

benefits. Sweetcom is also an excellent crop in a vegetable rotation program. Soil organic matter levels are increased and soil bome diseases which are endemic in sub-tropical and tropical areas under intense vegetable production are greatly reduced by sweet com which will provide viable crop rotations. This will assist in ensuring long term sustainability of the vegetable industries in these regions.

5. References

Australian Bureau of Statistics, 1995. ABS Canberra.

Brewbaker, J. L. (1981). Maize Improvement in relation to photoperiod sensitivity and incident solar radiation. Tech. Bull No. 59. ASPAC Food and Fibre Technology Centre, Taiwan.

Deuter, P. (1995). Heliothis Control - Queensland Experiences. Sweet Com Integrated Pest Management - Heliothis and Soil Pest Control Workshop, Cowra, NSW.

McMahon, C. R. (1991). Review of New Processing Opportunities in Queensland: Tropical Sweet Com Review. QDPI Workshop Report.

McMahon, R. and E.Corsan (1997). Opportunities for Improving the International Competitiveness in Producing and Processing Sweet Com in Australia.. DBIRD/QDPI Review.

Olsen, J.K., Blight, G.W. and D. Gillespie (1990). Comparison of yield, cob characteristics and sensory quality of six supersweet (sh2) com cultivars grown in a subtropical environment. AJEA 30, 387-393.

27

Olsen, J. K., McMahon, C.R., and G.L. Hammer, (1993). Prediction of Sweet Corn Phenology in Subtropical Environments. Agronomy Journal. 85, (2), 410-415.

Pataky, J.K. and P.R. Mosely (1995). Successful Use of Resistance to Control Disesses of Sweet Corn. Plant Disease 79, (12) 1256-1258.

Pullar D., Cadman R., Lewis, I. And P. Morey, (1993). Winning The Race: Being Internationally Competitive. A case study of the Australian sweet corn industry. Horticultural Policy Council, Case Study No. 7.

Smith, D. (1997). Sweet Corn Industry Workshop. Institute For Horticultural Development, Knoxfield, Victoria. (Unpublished).

28